There are many Gods in the different pantheons. Most people will simply pick a particular God that is compatable with the Goddess they have chosen, and simply use that God for all rituals and spells (Example: Isis and Osiris, Cerridwen and Cernunnos, etc.). Others prefer to vary the use of a name depending on what they are requesting. Example: If you are asking for calm or peace, I'm not sure that calling on Ares would be appropriate. This is where the variation would come in.

For now that is the best information I can give you. Hopefully, I'll find the time soon to type up all the information I have on the dieties (male and female) from almost every culture.